Thermodynamic change of state of a system in which there is transfer of heat across the boundaries of the system. Compare to adiabatic process.

A spring which is designed to achieve a fixed spring constant over a wide temperature range. Usually, this involves an alloy with high nickel content such as Ni-Span C. It is common for these springs to be stress relieved at elevated temperature after for ...

The transducer of any hygrometer, i.e. that part of a hygrometer that quantitatively "senses" atmospheric water vapor.

Anemometer whicb measures wind speed by measuring the degree of cooling of a metal wire heated by an electric current. A type of cooling power anemometer.

A forecast of the expected stage or discharge at a specified time, or of the total volume of flow within a specified Interval of time, at one or more points along a stream.

The direction, with respect to true north, from which the wind is blowing. Distinguish from magnetic wind direction. In all standard upper-air and surface weather observations, it is true wind direction that is reported.

Phase Shift Keying. A form of phase modulation of a data signal performed by a modem for transmission over dedicated wire or phone lines.

variable audio-modulated radiosonde developed at the Bureau of Standards and used by the United States weather services.

A measure of the degree to which the weather or climate of a region is favorable to the process of evaporation. Usually considered to be the rate of evaporation. under existing atmospheric conditions, from a surface of water which is chemically pure and h ...

Thermometer in which the difference in the rates of expansion with temperature of a liquid and its receptacle is used as a measure of the temperature. The liquid used may be ethyl alcohol, toluene, petroleum, or mercury.

A technique for making winds aloft observations in which two theodolites located at either end of a baseline follow the ascent of a pilot balloon. Synchronous measurements of the elevation and azimuth angles of the balloon. taken at periodic intervals, pe ...

A hydrometeor consisting of an aggregate of microscopic and more-or-less hygroscopic water droplets suspended in the atmosphere. It reduces visibility to a lesser extent than fog. The relative humidity of mist is often less than 95 percent.

The standard deviation (positive square-root of the variation) of the errors associated with physical measurements of an unknown quantity, or statistical estimates of an unknown parameter or of a random variable.

Winds which, over a small area, differ from those which would be appropriate to the general pressure distribution.

The time required for an instrument to registe 63.2% of a step change in the variable being measured.

A device for measuring the river stage. Also called stream gauge.

The total amount of water transferred to the atmosphere by evapotranspiration.

A direct-vision nephoscope constructed in the following manner: A grid-work of bars is mounted horizontally on the end of a vertical column and made free to rotate about the vertical axis. The observer rotates the grid and adjusts his or her position unti ...

An anemometer which measures wind speed by means of the properties of wind-borne sound waves. It operates on the principle that the propagation velocity of a sound wave in a moving medium is equal to the velocity of sound with respect to the medium plus t ...

Same as an upper air observation, but commonly used to refer to a single complete radiosonde observation.